Chemically, rhein is 9,10-dihydro-4,5-dihydroxy-9,10-dioxo-2-anthracene carboxylic acid having a structure of Formula I and diacerein is 4,5-bis(acetyloxy) 9,10-dihydro-4,5-dihydroxy-9,10-dioxo-2-anthracenecarboxylic acid having a structure of Formula II. Diacerein is widely used in the treatment of osteoarthritis and has a unique mode of action that differentiates it from non-steroidal anti-inflammatory drugs (NSAIDs) and other conventional forms of drug therapy.

Diacerein is practically insoluble in solvents such as water, alcohols, acetone, dichloromethane and chloroform, which are generally used in pharmaceutical preparations. Although diacerein can be administered by oral route but it cannot be completely absorbed by the digestive tract, and this incomplete absorption results in undesirable side effects such as, soft stools.
In order to overcome these problems, various derivatives, pharmaceutical compositions and specific galenic forms have been proposed in the literature. For example, European patent EP 243,968 describes a diacerein potassium salt, which is water-soluble and can be used in the preparation of compositions for parenteral administration.
EP904060 discloses pharmaceutical compositions of rhein or diacerein, wherein rhein or diacerein is co-micronized with sodium lauryl sulfate.
European Patent Nos. EP263083; 264989 and 446753 disclose controlled release or delayed release compositions like multiplicity of pellets coated with drug and coating membrane or granules of drug coated with polymers or loading polymeric particles of water swellable cross-linked polymer with drug.
U.S. Pat. Nos. 5,225,192 and 5,569,469 describe different poorly soluble medicaments supported on polymeric particles of water swellable cross-linked polymer with drug.
U.S. Pat. No. 5,952,383 and European Patent No. EP 862423B1 describe pharmaceutical compositions of diacerein, rhein and their salts along with liquid support systems like oils, suspending agents, homogenizing agents and other excipients.
However, none of the formulations discussed above teach liquid oral dosage form of rhein or diacerein. Currently, diacerein is marketed as capsules in 50 mg strength under the trade name Art 50® and given twice a day. The capsule forms are, however, difficult to swallow, especially for geriatric patients. Further, the fear of swallowing, or choking on such solid shaped articles is still a concern in certain populations especially, geriatrics. It is estimated that almost 50% of the population have problems of swallowing tablets or capsules (Seager in Journal of Pharmacol. and Pharm. Pages 375-382, 1998). The capsule dosage forms become sticky when wetted by saliva, and if a patient experiences difficulty in swallowing on its first attempt, then the capsule must often be discarded. Furthermore, if a capsule partially dissolves in a patient's mouth, as can result from unsuccessful swallowing or the capsule getting stuck in the orthodontic appliance, the resulting very unpleasant taste can make it difficult to persuade the patient to take another dose. Additionally, these dosage forms are difficult to carry, store and handle. All these difficulties associated with capsules result in decreased patient compliance.
Liquid oral preparations are useful for obvious reasons. Firstly, it is preferable for patients either with physical disabilities or incapacitated. Secondly, patient compliance is often a problem with oral solid dosage forms, especially with young children and senior citizens. Thirdly, liquid compositions would help a pharmacist to dispense the correct amount of drug without resorting to sub-division of a larger dosed tablet into pieces. Fourthly, as solutions are homogenous, the medication is uniformly distributed throughout the preparation. A drug administered in solution is immediately available for absorption from the gastrointestinal tract and is more rapidly and efficiently absorbed than the same amount of drug administered in a tablet or capsule.